The invention relates to a mixing element for a static mixer of plastic including an installation body for installation into a tubular mixer housing. Such a mixer as well as the associated mixer housing can be connected to the outlets of a multicomponent cartridge as in WO 2008/113196 A1 and can in their totality represents a cartridge arrangement as is shown in FIG. 2 of WO 2008/113196 A1.
The mixing element, in particular its installation body, has a longitudinal axis which is aligned in the direction of a fluid flowing into the installation body so that a mixing space can be spanned by the installation body in the inner space of the mixer housing. The mixing space has a cross-sectional flow area in a plane normal to the longitudinal axis which essentially corresponds to the cross-sectional flow area of the tubular mixer housing. The installation body includes a wall element for the division and/or deflection of the fluid flow into a direction deviating from the longitudinal axis.
Such a static mixer is, for example, known from EP 1 426 099 B1. In this static mixer, two components are mixed with one another by means of a plurality of mixing elements of the same type in a three-part mixing process in which the material is first divided, then spread and displaced. This mixing process has to be carried out several times depending on the physical properties of the components. For this reason, the static mixer contains a plurality of installation bodies of the same construction arranged behind one another. These mixers are in particular used for the mixing of small quantities of the components, that is a few milliliters up to approximately 1,000 milliliters. Accordingly, these mixers have a mixing space with a diameter of less than 16 mm with a length of more than 50 mm. This has the consequence that the wall thicknesses of the wall elements of this mixer can amount to less than 1 mm, often even less than 0.5 mm.
Such a static mixer in accordance with EP 1 426 099 B1 of plastic is preferably manufactured in an injection molding process. The manufacture of a mixer of 30 mm length with a wall thickness of less than 3 mm using the injection molding process, as shown in FIG. 1 of this patent, was previously not possible since the flow path from the injection point of the injection molding tool up to the oppositely disposed end of the mixer would require internal tool pressures which are too high. To be able to manufacture a static mixer having such small wall thicknesses economically in the injection molding process, each installation body is connected to the adjacent installation body via bar elements. These bar elements allow the polymer melt in the injection molding tool to move from one installation body to an adjacent installation body and to maintain the inner tool pressures below 1000 bar so that a failure of the injection molding tool can be prevented. It must be noted that an inlet element is interposed before the installation bodies. The inlet element contains the two inlet passages which introduce the components from the cartridge outlets into the mixer housing. The mixing element contains installation bodies. The components are deflected, divided and recombined by the installation bodies, whereby a mixing of the components takes place. The components are thus present as a uniformly mixed filler material at the outlet end.
The mixer of WO 2008/113196 A1 has a configuration in accordance with which a lead of one component is prevented in that a constriction is provided in the flow passage, that is a restriction effect is deliberately installed. FIG. 13 of WO 2008/113196 A1 shows that a bar element is provided for this purpose in the inlet region of the mixer adjoining its inlet passage, said bar element forming a flow obstruction and providing the deflection of the flow around this bar element. The component flowing at the left side thus has a longer flow path imposed on it than the component flowing at the right side. In accordance with another embodiment which is shown in EP 0 885 651, a separation bar is provided over each of the two inlet openings. This separation bar is flowed around by the component flowing through the corresponding inlet opening. The volume flows of the two components also differ in this embodiment. The first component having the larger volume flow is guided adjoining the separation bar by bar elements parallel to the outer surface of the adapter element in the direction of the inlet opening of the second component. The second component which has a smaller volume flow is taken up by the first component and brought into contract even before the entry into the mixing element. This means that the first component having the larger volume flow reaches the mixer with a delay in relation to the second component, that is its flow is delayed by an additional path length.
In the document EP 0 723 807 A2, a variant is shown in accordance with which the inlet chambers have different volumes when the components are present in a mixing ratio not equal to 1:1. These inlet chambers take up the components conveyed from the cartridge before they enter into the mixing element. The inlet chamber of the first component which forms the larger volume flow has a larger volume than the inlet chamber of the second component which forms the smaller volume flow. When the first component thus moves into the inlet chamber, the inlet chamber is first completely filled before the component reaches the first mixing element of the static mixer. The second component simultaneously flows through the second inlet chamber which has a substantially smaller volume. The volume ratio can thus be set such that the first component and the second component reach the first mixing element simultaneously.
The component which has a higher volume share is also dammed in accordance with EP 0 584 428. The flow path is interrupted by a plate at the inlet of the static mixer for this purpose. A slit-like opening is provided in this plate through which the components which have filled up the reservoir space disposed in front of it move into the static mixer. A lead of the component having the larger volume flow is hereby suppressed.
It can thus be said in a generalizing manner that the volumes which are located between the cartridge and the mixer should be adapted to the corresponding mixing ratios in order to be given as little a lead as possible to avoid material being obtained mixed in an unusable manner. The first approach is therefore to adapt the cross-sectional areas of the feed lines in accordance with the desired mixing ratio. If, however, very different mixing ratios are present, the cross-sectional area for the component having the smaller volume flow can, however, no longer be manufactured. An additional volume, for example an inlet chamber as described in EP 0 723 807 A2 or a chamber at the inlet end of the mixing element as described in EP 0 584 428 A1, is therefore provided to the component having the larger volume flow.